There are exceptions, of course–your personal safety or the safety of another being the primary examples–but generally speaking? It is not a good idea to lie on the internet.
People will find out. They will cross-check, cross-reference, research, ask mutual friends, or read old chat logs. The truth will eventually be uncovered, and then your social life is pretty much fucked.
We talk to each other. Communicate with each other. Interact. Poke at each other to see if we’re all still breathing.
We’re a community, not isolated individuals.
Don’t lie to us. We’ll know.